tuber(redirected from tuber ischii)
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tuber,enlarged tip of a rhizome (underground stem) that stores food. Although much modified in structure, the tuber contains all the usual stem parts—bark, wood, pith, nodes, and internodes. The eyes of a potato tuber are nodes where sprouts appear, and they are arranged in the same spiral pattern characteristic of buds on an aerial stem.
a modified shoot of a plant with a thickened stem consisting of one or several internodes (sometimes a thickened hypocotyl or part of the root). Tubers located above the ground are usually green and have leaves (such as kohlrabi and some tropical orchids). Underground tubers usually have the leaves reduced to very small scales that fall off early; the buds that form in their axils are called eyes. Tubers usually store nutrients, most often starch and other carbohydrates, and more rarely, oils (as in chufa).
Tubers develop from the parenchymatous cells of the phloem and xylem, and, less often, from the pith. They can appear on the main axis of the plant (usually at the base) as well as on lateral shoots (as in field horsetail and marsh woundwort) and on underground shoots, or runners (as in potatoes and Jerusalem artichoke). Tubers in the form of hypocotyls are found on cyclamen and certain Umbelliferae such as Chaerophyllum, tuberiferous caraway (Carum bulbosa), Corydalis, and Eranthis. Tubers usually serve for propagation. After the runners atrophy, the buds sprout and adventitious roots form, and the tuber develops into a new plant. In some plants aboveground tubers develop into inflorescences. In these cases, small tubers with thickened axes form in the axils of the bract. The buds of the tubers produce from two to four leaves, and, after falling off the plant, the buds take root, forming new plants (viviparous plants). In Ficaria the sprouting of the tubers that develop in the leaf axils and the formation of adventitious roots take place after the tubers fall off the plant, usually after wintering. Plants whose tubers are used as food for man, or feed for animals, or for industrial raw materials are called tuber crops.
L. V. KUDRIASHOV